Fetal Development
From Fertilization to Birth
Conception occurs when a woman's egg is fertilized by a man's sperm. The union of egg and sperm usually occurs in the woman's fallopian tube. The cell, now containing a complete set of genetic material, begins to divide into more cells while traveling down the fallopian tube to the uterus. This journey takes about a week. By the eighth day after fertilization the ball of cells has begun to attach itself to the wall of the uterus where it can obtain nutrients to continue its growth. The growing body of cells is called an embryo from the time of attachment in the uterus until it begins its ninth week of growth. Thereafter, it is appropriately referred to as a fetus. "Fetal age" in this website refers to the time from conception. "Gestational age" is two weeks longer than the fetal age because it is counted from the beginning of the woman's last menstrual period. Fetal size is measured by weight and by length. Length is measured from the top of the head (crown) to the rump, called crown-rump length (CRL). The descriptions of fetal development are not intended to be complete. For more information and readings on fetal development, go to the reference lists by clicking on the link on the right side of the screen. The descriptions of fetal development are not intended to be complete. For more information and readings on fetal development, go to the reference lists.
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